Cementing method for wells



A ril 28, 1964 o. J. MCCULLOUGH CEMENTING METHOD FOR WELLS F iled June 28, 1961 INVENTOR.

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ATTORNEY United States Patent 3,130,785 CEMENTING METHQD FOR WELLS Otis J. McCullough, McCullough Tool (10., R0. Box 2775, Houston, Tex. Filed June 28, 1961, Ser. No. 122,059 4 Claims. (Cl. 166-46) This invention relates to improvements in the cementing of wells, particularly oil and gas Wells.

The cementing of oil and gas wells involves the introduction of cement between the wall of a well bore and a pipe string which is inserted in the well bore after it has been drilled. In the conventional procedure the well bore is drilled through a lithologic section which normally comprises a series of earth formations, some of which may contain salt water, others gas, and still others oil. These fluid-containing strata are commonly separated by impervious strata, such as shales and other rocks which normally form fluid-barriers or seals between the various fluid-containing formations. When the bore hole has intersected such a section containing these several strata, communication will be established through the impervious rock strata between the various fluid-containing strata. The principal purpose of cementing between the pipe string extending through such a section and the wall of the bore hole is to seal-off communication between the formations containing undesirable fluid, such as salt or fresh Water, or even gas in some cases, and those containing the desired fluids, particularly oil.

The provision of an effective seal by means of cementing is critical to the obtaining of efficient production from the well. If the seal is ineffective for any reason, water or other undesirable fluids will migrate through the bore hole between the formations and in many instances will drown out the oil-containing sands or other type strata and, in general, will interfere with the production of the oil or gas, as the case may be, so as to render the production uneconomic and in some cases, completely impractical.

Obtaining an elfective seal with normal cementing procedures proves to be a very difficult operation in numerous instances due to many conditions encountered in the drilling of the well. These may include cavities in the earth formations and high porosity rocks. The chemical composition of the rocks lining the bore hole and fluids contained therein will often have a deleterious effect upon the setting characteristics and other essential properties of the cement. Other conditions eflecting the character of the seal may be the temperature of the bore hole and other conditions well-known to those skilled in the art.

In order to overcome these difliculties in effecting a good cement job, many variations in composition of cement, cementing procedures, and the like, are employed. When the well is then tested before being put into production and leakage of undesirable fluids is found, it frequently becomes necessary to perform what are known as squeeze jobs, by means of which additional cementing operations, conducted at high pressures and in accordance with various known procedures, are employed in an attempt to close-off the leaks.

The leakage which thus occurs is commonly referred to in the art as channeling and occurrence of channeling, for whatever reason, is one of the most annoying and troublesome conditions occurring in the completion of oil and gas wells. When channeling occurs, considerable effort is required to correct the condition, frequently at great expense and often with substantial loss of production, sometimes to the extent of causing abandonment of the well.

' The channeling encountered so frequently in cementing operations results, in my opinion, from the fact that 3,130,785 Patented Apr. 28, 1964 very few bore holes are ever perfectly straight throughout their length, and particularly in the producing sections where interspersed relatively hard and relative soft strata occur. In almost all cases where Wells are drilled by the rotary method, continuous surveying must be carried on during the course of drilling to repeatedly correct for the deviation from the vertical which commonly occurs as the well drilling proceeds. Usually every effort is made to limit the inclination of the well bore at any point to one degree or less, and common practice is to run a survey tool every feet or so, in order to determine whether deviation is occurring and to make appropriate corrections therefor. Despite the care which is exercised in attempting to keep the hole perpendicularly straight throughout the drilling, most bore holes will be defined by a series of convolutions or bends, some sharper than others, depending upon the amount of deviation which may have occurred before correction. Also the orientation of the bends or convolutions will vary from point to point along the bore hole. FIG. 1 in the drawing illustrates, diagrammatically, a section of bore hole through the producing section of a typical well which is illustrative of the generally sinuous shape which frequently characterizes the bore hole. There are many obvious variations in the particular shape of the bends or convolutions which occur in different wells, but a shape as illustrated in FIG. 1 will serve to illustrate the problem which has been solved in accordance with this invention.

When a string of pipe, such as casing, is run into a well bore of the shape of that illustrated in FIG. 1, the pipe will necessarily be in contact at numerous points with the wall of the well bore due to the bends and convolutions thereof. This condition is illustrated in FIG. 3 where it will be seen that the pipe is in contact with the wall of the well bore at a number of points along the bore. When a pipe string is thus inserted in a well bore, as illustrated, the weight of the pipe string will cause the pipe to press strongly against these points of contact so as to prevent the entrance of any substantial layer of cement between the pipe and the wall of the bore hole at these points or areas of contact. At most, any cement which might penetrate these areas of contact will provide a very thin layer and will produce weak bonds which will prove ineffective as seals in the subsequent operation of the well.

Heretofore, pipe strings have been equipped with centralizers when they are run into the well bore in an effort to effectively center the pipe in the bore hole so that a uniform layer of cement of sufficient thickness can be introduced between the pipe and the bore wall. However, while this may be effective in a bore hole which is substantially straight throughout its length, it is of little value in a bore hole having the more common, generally sinuous form previously described, since bends in the bore wall may occur between centralizers. Moreover, because of the fact that the bore holes are frequently not absolutely perpendicular, the pipe, by reason of its weight, will simply move over to one side or the other of the bore hole compressing the centralizers against the bore wall in the areas of contact and a condition will result which is quite similar to that illustrated in FIG. 3.

It is, therefore, a primary object of this invention to provide an improved cementing method for oil and gas wells which overcomes the principal problems heretofore experienced in cementing which result in channeling between fluid-containing formations.

It is an important object of this invention to provide an improved cementing method which overcomes the problem of channeling due particularly to the crookedness of the bore hole.

In accordance with the present invention, the improvement comprises the step, conducted prior to the running of the pipe string and cementing in the conventional manner, of forming annular grooves or recesses in the wall of the bore hole in those impervious earth strata which separate formations containing desired well fluids from those containing undesired well fluids. Thereafter, when the pipe is run into the well and cement is introduced in the usual manner, these annular grooves will be filled with cement and form effective annular seals between the pipe and the impervious earth strata, which will effectively seal-off formations containing undesired fluids from those containing the desired fluids.

The grooves may be formed in any conventional manner by conventional means. One method, which employs entirely conventional apparatus and procedures, is to run a known type of underreamer or wall scraper on a drill string into the bore hole before the pipe is run, and to cut the desired grooves in the selected impervious rock strata. These strata will have been located from the curves exhibited on the usual electric log of the bore hole, which is commonly obtained after drilling is completed and before the pipe is run into the well bore prior to cementing. These logs are very accurate in locating the depth positions of fluid-containing strata, as well as the interspersed non-fluid-containing or impervious strata. Moreover, the logs also serve to indicate the character of the fluid-containing formations, that is, whether a formation is a water-or a hydrocarbon-containing formation, so that it is a relatively simple operation to determine the exact positions of the impervious strata in which the grooves are to be located.

When grooving of the bore hole has been completed, pipe may be run into the bore hole and cemented in the conventional manner, the cementing being conducted through at least that section of the bore hole which contains the annular grooves.

Further and more specific objects of this invention will become more readily apparent from the following detailed description when read in conjunction with the accompanying drawing which illustrates, more or less diagrammatically, the stages in the cementing of a well in accordance with this invention.

In the drawing:

FIG. 1 illustrates, diagrammatically, the generally sinuous character of a well bore at the completion of drilling, the bore being shown extending through a generally characteristic lithologic section including fluid-containing earth formations and relatively impervious strata which separate the several fluid-containing formations;

FIG. 2 illustrates the same bore hole after cutting of the annular grooves in the several impervious strata has been completed;

FIG. 3 illustrates the next stage of operation in which a pipe string has been run into the bore hole preparatory to cementing;

FIG. 4 illustrates the completed cementing stage; and

FIG. 5 is a cross-section taken along line 5-5 of FIG. 4.

Referring to the drawing, FIG. 1 shows a bore hole B which has been completed by conventional drilling through the various earth formations in a lithologic section from which production is to be obtained. The sinuous shape of the bore hole is, as has been mentioned previously, generally illustrative of the shape of a bore hole which has been drilled through such earth strata by the rotary method. When the drilling of the bore hole has been completed, a survey tool will be run into the well bore and through the section comprising bore hole B in conformance with conventional practice. Such a survey tool may be any one of the various wellknown devices for surveying bore holes to determine the depth position, thickness, and character of the different strata which have been intersected by the bore hole. As indicated previously, there are various electric surveying systems employed for this purpose, it being understood that the details of such systems or devices do not, of themselves, form a part of this invention.

As indicated in FIG. 1, bore hole B intersects a series of earth formations which include water-containing formations W W and W oil-containing formations O and O gas-containing formation G and a series of impervious rock strata such as the shale sections designated S S S S S and S These shale sections intervene between the several fluid-containing formations and serve normally to seal-off each of the fluid-containing formations from the others. The intersection of all of these earth formations by the bore hole will, of course, place the various fluid-containing formations in communication with each other unless effective sealing is accomplished, as will be subsequently described.

Having located the various strata, particularly the impervious strata along the well bore by means of the survey tool, the next stage of operations in accordance with this invention is to run an underreamer or wall scraping tool, of any well-known and generally conventional form, into the well bore on a drill string, and to operate this cutting or scraping tool to cut at least one annular groove, designated A A A A A and A in the wall of the bore hole within the body of each of the respective shale sections S to S as seen in FIG. 2.

When cutting of these annular grooves is completed, the cutting tool is removed from the well bore and a string of pipe P, which may be a casing, liner, tubing or any other conventional string of pipe, will be run into the bore hole in the usual manner to extend through the section of bore hole B which traverses the several earth formations previously described, this stage of operations being illustrated in FIG. 3. It will be noted that due to the sinuous configuration of the bore hole, pipe P will contact points along the wall of the bore hole at a number of places, indicated by the letters C C C and C with the result that when cement D is introduced into bore hole B between pipe P and the wall of bore hole B (FIG. 4), the cement will not penetrate between the pipe and the wall of the bore hole at these points of contact or, at best, will comprise a very thin section of cement, as has previously been explained.

When the pipe has been put in place in the well bore, cementing will be conducted in the conventional manner, cement D being forced downwardly through the bore of pipe P through a conventional cementing valve and up into the annular space provided between the exterior of pipe P and the wall of bore hole B. This cement will, as illustrated particularly in FIG. 4, not only fill the annular space, but will also necessarily flow into and fill annular grooves A to A Thus, as will be seen, for ex ample, with reference to point of contact C even though little, if any, cement may be present between the pipe and the wall of the bore hole at this point, nevertheless, groove A will provide a substantially continuous collar of cement in shale strata S above point of contact C while a similar collar of cement will be formed in groove A about the pipe in shale strata 8,, thus sealing-off gascontaining formation G from communication with any other section of the well bore. Similarly, the cement in groove A in combination with that in groove A will seal off water-containing formation W from communication with any other part of the well bore. The cement in grooves A and A will likewise seal off oil-containing formation 0 from communication with water-containing formations W and W Thus, in each instance, each fluid-containing formation will be sealed off by the cement collars or rings formed in the impervious strata which lie on each side of that particular fluid-containing formation. It will be seen, theerfore, that the fact that no cement may be present to form a seal between the pipe and the well bore at point of contact C the cement collars formed, as described, will nevertheless effectively assure complete sealing against migration of fluids into or out of this strata.

It will be understood that any combination of seals may thus be formed along the well bore. In some instances, it may be necessary only to seal above and below a single fluid-containing formation where only one such formation exists in a section from which desired fluid is to be obtained. It will also be evident that various combinations of seals may thus be effected at any number of selected locations along the well bore, depending upon the relative positions of the various earth formations which are to be segregated from each other or connected together, as the case may be. Moreover, it will be evident that the particular shape of the bore hole will no longer present any special problem, so far as effecting perfect sealing by means of otherwise conventional cementing procedures.

While the use of an underreamer or scraping tool is probably most eflicient for purposes of forming the annular grooves, it will be recognized that other devices, such as high velocity jets of fluid, with or without abrasive materials, may also be employed.

The dimensions of the grooves will obviously be variable, depending, in general, upon the nominal diameter of the bore hole and the character of the earth strata in which they are to be located. Ordinarily, an annular groove having an external diameter of from three to six inches greater than the nominal diameter of the bore hole and having an axial length of only a few inches, will usually be suflicient to assure effective sealing, since the annular collar of cement thus provided in the impervious strata will be of sufllcient depth and thickness to assure a good closeoflf between the pipe and wall of the bore hole. The grooves will be made generally concentric with the bore hole and more than one groove may be formed in any stratum, if desired.

From the foregoing, it will be seen that I have provided a relatively simple improvement in conventional cementing methods for oil and gas wells by which the foregoing objects and advantages will be attained and, in particular, channeling, which occurs so frequently in conventional cementing operations, will be obviated to a maximum degree.

What I claim and desire to secure by Letters Patent is:

1. In the cementing of pipe strings in well bores which intersect a series of fluid-containing earth formations, said series including relatively impervious earth strata interspersed between said fluid-containing formations, the improvements for preventing channeling between fluid-containing formations which comprises, forming annular radially extending grooves in the wall of the well bore in the relatively impervious strata which separate fluidcontaining earth formations from each other, inserting a pipe string through said fluid-containing earth formations and the intervening relatively impervious earth strata, and introducing cement to fill the space and seal between the pipe string and at least that portion of the wall of the well bore including said annular grooves.

2. In the cementing of a pipe string in a well bore which intersects a series of earth formations some of which contain desired fluids and others undesired fluids, said series including relatively impervious earth strata interspersed between said fluid-containing formations, the improvements for preventing channeling between the fluid-containing formations which comprises, forming annular radially extending grooves in the wall of the well bore in the relatively impervious strata which separate those earth formations containing desired fluids from those containing undesired fluids, inserting a pipe string through said fluid-containing earth formations and the intervening relatively impervious earth strata, and introducing cement to fill the space and seal between the pipe string and at least that portion of the wall of the well bore including said annular grooves.

3. In the method of cementing of a pipe string in a well bore which intersects a series of earth formations including fluid-containing formations interspersed with relatively impervious strata, the improvement for preventing channeling between fluid-containing formations which comprises, surveying the bore hole to locate impervious strata which intervene between fluid-containing formations between which it is desired to prevent fluid communication, forming annular radially extending grooves in the wall of the bore hole in said intervening impervious strata, inserting a pipe string into the bore hole to extend through said fluid-containing formations and said intervening impervious strata, and introducing cement to fill the space and seal between the pipe string and at least that portion of the wall of the bore hole which includes said fluid-containing formations and said intervening impervious strata having said grooves therein.

4. The method according to claim 2, wherein the for' mations containing desired fluids are hydrocarbon-containing formations, and those containing undesired fluids are water-containing formations.

References Cited in the file of this patent UNITED STATES PATENTS 1,807,050 Stolz May 26, 1931 2,092,041 Armentrout et al Sept. 7, 1937 2,780,289 Garrison Feb. 5, 1957 2,858,107 Golmerauer Oct. 28, 1958 

1. IN THE CEMENTING OF PIPE STRINGS IN WELL BORES WHICH INTERSECT A SERIES OF FLUID-CONTAINING EARTH FORMATIONS, SAID SERIES INCLUDING RELATIVELY IMPERVIOUS EARTH STRATA INTERSPERSED BETWEEN SAID FLUID-CONTAINING FORMATIONS, THE IMPROVEMENTS FOR PREVENTING CHANNELING BETWEEN FLUID-CONTAINING FORMATIONS WHICH COMPRISES, FORMING ANNULAR RADIALLY EXTENDING GROOVES IN THE WALL OF THE WELL BORE IN THE RELATIVELY IMPERVIOUS STRATA WHICH SEPARATE FLUIDCONTAINING EARTH FORMATIONS FROM EACH OTHER, INSERTING A PIPE STRING THROUGH SAID FLUID-CONTAINING EARTH FORMATIONS AND THE INTERVENING RELATIVELY IMPERVIOUS EARTH STRATA, AND INTRODUCING CEMENT TO FILL THE SPACE AND SEAL BETWEEN 